The present invention generally relates to a display for and method of displaying electrograms received from an implantable cardiac device. The present invention more particularly relates to such a display and method which locates selected cardiac events at a predetermined location on a display screen to facilitate easier discernment of selected cardiac events and intervals.
Implantable cardiac devices are well known in the art. They may take the form of implantable defibrillators or cardioverters which treat accelerated rhythms of the heart such as fibrillation or implantable pacemakers which maintain the heart rate above a prescribed limit, such as, for example, to treat a bradycardia. Implantable cardiac devices are also known which incorporate both a pacemaker and a defibrillator.
A pacemaker may be considered as having two major components. One component is a pulse generator which generates the pacing stimulation pulses and includes the electronic circuitry and the power cell or battery. The other component is the lead, or leads, which electrically couple the pacemaker to the heart.
Pacemakers deliver pacing pulses to the heart to cause the stimulated heart chamber to contract when the patient""s own intrinsic rhythm fails. To this end, pacemakers include sensing circuits that sense cardiac activity for the detection of intrinsic cardiac events such as intrinsic atrial events (P waves)and intrinsic ventricular events (R waves). By monitoring such P waves and/or R waves, the pacemaker circuits are able to determine the intrinsic rhythm of the heart and provide stimulation pacing pulses that force atrial and/or ventricular depolarizations at appropriate times in the cardiac cycle when required to help stabilize the electrical rhythm of the heart.
Pacemakers are described as single-chamber or dual-chamber systems. A single-chamber system stimulates and senses the same chamber of the heart (atrium or ventricle). A dual-chamber system stimulates and/or senses in both chambers of the heart (atrium and ventricle). Dual-chamber systems may typically be programmed to operate in either a dual-chamber mode or a single-chamber mode.
Implantable cardiac stimulation devices conventionally include an internal telemetry circuit permitting the devices to communicate with an external programmer. The external programmers also include a telemetry circuit with an external antenna or xe2x80x9cwandxe2x80x9d which is held over the implant site to allow the communication between the programmer and the implanted device. With the communication channel thus established, the programmer permits the attending medical personnel to set device operating modes and stimulation and sensing parameters within the device. The communication channel also permits the device to convey to the external programmer operating and sensed physiological data for display. The physiological data may include an intracardiac electrogram (IEGM) or a plurality of IEGMs sensed across different portions of the heart. The IEGMs may be prestored in the device and conveyed to the programmer responsive to a suitable external command from the programmer. Along with the IEGMs, event markers may also be transmitted. The event markers represent sensing of cardiac events or the delivery of stimulation pulses. The event markers may represent sensing of intrinsic events such as P markers for P waves or R markers for R waves and delivery of stimulation pulses such as A markers for atrial stimulation pulses and V markers for ventricular stimulation pulses. When displayed, the event markers are aligned with their respective or corresponding event. The result is that physicians are provided with electrogram displays that provide more insight into the operation of the devices, the interaction of the device with the patient, and the underlying rhythm.
External displays, such as may be found in programmers for pacemakers and defibrillators display in real time or stored electrograms. Typically, the display scrolls while the electrograms, markers and interval information are being displayed on the display screen. While the electrograms scroll across the screen, event markers and associated interval information can occur anywhere on the screen. Since the electrogram display is being updated continuously, there is little time for the user to internalize the relative timing between events. As a result, most users must resort to making a printout of the displayed information to enable an analysis of the timing sequences in the electrograms.
The present invention provides a different approach to display electrograms. Instead of scrolling the display, the display is triggered by a cardiac event. The trigger may be either an intrinsic sensed event or an extrinsic paced event. As a result, the triggering event occurs in the same place on the display screen, locking the events and timing intervals to be discerned to that point.
In a single chamber device, there is usually a single IEGM channel to display. Therefore, the trigger may be a sensed P wave or R wave marker or a ventricular pacing pulse or atrial pacing pulse marker.
For a dual chamber device, where more than one IEGM channel is displayed, the user may select which IEGM channel to use as the triggering channel. For either a single chamber device or a dual chamber device, the user may also select the triggering event. For example, if the user is interested in measuring an AV delay, then either an A marker or P marker may be used as the triggering event. If, however, the user is more interested in discerning VA intervals, then either a V marker or R marker may be used as the triggering event.
The trigger point may be located at any desirable position on the horizontal axis of the display screen. Three positions which may provide the most benefit may be the one-eighth, middle or seven-eighths horizontal positions on the display screen since they allow observing both post-trigger and pre-trigger IEGM information.
In a special mode, the current waveform could be overlayed on top of a previous one or more waveforms, all having a common trigger event. The one or more previous waveforms could be distinguished by using different display characteristic (e.g., trace color, or other line attributes).
In the event that the IEGM telemetry has been received without event markers during a continuous time-out period, the display may then revert back to a scrolling display of the IEGM information. A warning message may also be presented to advise, for example, that pacing has been turned off or that severe under-sensing is occurring.
In accordance with the broader aspects of the present invention, the display includes a receiver that receives an electrical signal representing the electrical activity of a heart wherein the electrical signal includes event markers identifying occurrences of at least one type of cardiac event represented in the electrical signal. A display control circuit coupled to a display and to the receiver locates the display of the at least one type of cardiac event at a predetermined position on the display in response to the event markers.
As a result, the event marker within the electrical signal is detected. Responsive to such detection, the electrogram is displayed on the display with a selected cardiac event within the electrogram being at a predetermined location on the display.